1. Field of the Invention
The present invention relates to an image forming apparatus and a control apparatus realized by a distributed control system.
2. Description of the Related Art
One CPU performs centralized control in printer device control of an image forming apparatus adopting an electrophotographic system. However, a higher-performance CPU is required as a result of an increase in the load of the CPU due to control-based centralization. Furthermore, communication cables (communication lines) need to be laid out to a control load driver unit distant from the CPU board along with the increase in the control load of the printer device, and a multiplicity of long, large communication cables are required. To solve the problems, a control format of dividing the control modules constituting the electrophotographic system into individual sub CPUs is drawing attention.
For example, Japanese Patent Laid-Open No. 2000-071819 proposes hierarchically disposing functional modules in a vehicle to perform distributed control, and Japanese Patent Laid-Open No. 2006-171960 proposes applying a similar hierarchical control structure to a robot/automation device. The plurality of sub CPUs include communication units that operate the entire system. Furthermore, in Japanese Patent Laid-Open No. 2006-171960, a control network for communications between functional modules establishes individual communication networks layer by layer. In this way, the establishment of a more stable control network by distributing the load is proposed.
To apply the proposed control network to the image forming apparatus, the increase in the cost caused by the distribution of the load needs to be minimized. Particularly, an effect of cost reduction by reducing the number of components on CPU circuit boards is large in the plurality of circuit boards mounted on one image forming apparatus. To realize this, a multiplicity of CPU vendors manufacture products including clock oscillators in the CPU, and systems using the products are also on the market.
However, there are the following problems in the built-in clock oscillators. For example, the built-in clock oscillators are less accurate compared to general clock oscillators, and there are individual differences in the built-in clock oscillators in the same type of CPUs. As a result, when a plurality of CPUs individually control actuators such as stepping motors, an error occurs in the speed between the stepping motors that control the conveyance of paper due to an error in the built-in clock oscillators, and mutual pulling of paper, flexures, etc., occur. Furthermore, time measurement results may be different between the CPUs in the measurement of a predetermined time. This causes a paper jam or a color deviation. Therefore, a system without the speed difference or the error in the time control between the CPUs is required in the image forming apparatus that realizes the distributed control.
Consequently, Japanese Patent Laid-Open No. 2000-078891 proposes a motor control apparatus that stores data related to a motor excitation signal sequence in a memory and that outputs the data in the memory to a control target motor as an excitation signal. Japanese Patent Laid-Open No. 2001-119996 proposes a motor acceleration/deceleration control method of a distributed control system that selects a solution of a linear operational expression from a deceleration time between an activation pulse speed and a motion pulse speed or selects an arithmetic method from the linear operational expression and that computes a pulse speed during acceleration/deceleration that is a next acceleration/deceleration process transition time. However, the control methods are for a single CPU, and an error between motor controls in a plurality of CPUs is not taken into consideration. For example, an error occurs in the speed between the stepping motors that control the conveyance of paper, and the error causes problems, such as mutual pulling of paper and flexures.